Most data processing systems in use today include some form of storage sub-system. In a personal computer, the storage sub-system often consists of nothing more than a single storage medium, such as a magnetic disk, attached to a circuit board in the central processing unit, which controls access to the storage medium. In more complex enterprise data processing systems, the storage sub-system may comprise numerous, diverse storage devices. For many years it was common practice for each such storage device to be attached to and controlled by a single processing unit, or “server,” which serviced other units through a network connection. Such a network of storage servers is commonly referred to as a storage area network, or SAN. Although other units could potentially access any given storage device through the attached server, this architecture creates many single points of failure and physically limits storage expansion. In recent years, though, storage virtualization techniques have emerged that allow a data processing system to divorce storage devices from the bonds of a single processing unit. In a virtual storage system, dedicated software assumes storage management responsibilities traditionally reserved for the operating system of an attached processing unit. But this dedicated software also assumes additional responsibilities, including responsibility for creating and managing “logical storage volumes.” Hence, this dedicated software is sometimes referred to as a “storage volume controller (SVC).” Unlike conventional storage devices, a logical storage volume may span many physical storage devices, even if no constituent storage device is attached to a central processing unit. The SVC implements a virtual interface so that a logical storage volume looks like any other conventional storage device to the other components of a data processing system, regardless of the composition or configuration of the underlying physical storage hardware. Moreover, the composition and configuration of the underlying physical storage hardware can change at any time, while the virtual interface insulates the other components from the physical changes. And while most of the preceding discussion presumes that the SVC's virtual interface replaces a server in a SAN, U.S. patent application Ser. No. 10/922,281 clearly demonstrates that storage virtualization technology also can be applied to peer-to-peer (P2P) networks.
Advanced storage virtualization technologies also attempt to manage network bandwidth to provide a predictable quality of service for priority users, and some provide additional storage to the data processing system on demand. To take advantage of such features, though, an administrator must specify threshold requirements and reserve resources in advance. An administrator also must update storage requirements manually, and must add storage to the SAN manually before the storage virtualization system can provide storage on demand. These auto-provisioning techniques are not suitable for SVCs in a P2P network, since such a network is decentralized and no single user has sufficient access or control to administer the auto-provisioning requirements.
The cost and reliability of storage devices can vary widely, but all inevitably fail at some point during their service life. In practice, particularly in an enterprise context, some types of data often are deemed more critical than other types, and resources can be maximized by balancing the importance of the data with the cost and reliability of potential storage devices. Current storage virtualization technologies provide an effective means for integrating numerous, diverse storage devices into a coherent and robust storage system, but no available system yet addresses this need to match data with a storage device that is appropriate to the importance of the data.